1. Field of the Invention
The present invention relates to the technical field of TFT-LCD (Thin Film Transistor-Liquid Crystal Display) liquid crystal displaying, and in particular to an LED (Light Emitting Diode) light bar and a backlight module of liquid crystal display device.
2. The Related Arts
A liquid crystal display is commonly abbreviated as LCD, and the operation principle is placing liquid crystal molecules between two parallel pieces of glass. A plurality of tiny vertical and horizontal conductive wires is arranged between the pieces of glass and change of direction of the liquid crystal molecules is controlled through application of electricity so as to refract light out to form an image. The liquid crystal display is now widely used due to various advantages of being compact in size, saving of power, and being free of radiations. Most of the liquid crystal display devices that are currently available in the market are backlighting liquid crystal display devices, which generally comprise a liquid crystal panel and a backlight module. The backlight module is generally divided into two categories, including edge backlight module and direct backlight module, for supplying back light to a liquid crystal display screen. The direct backlight module arranges a light source, such as CCFL (Cold Cathode Fluorescent Lamp) or LED (Light-Emitting Diode), on a back side of the liquid crystal panel, which have the disadvantages of arrangement and wire layout being complicated, requiring more light sources, and high cost. The edge backlight module arranges a LED light bar at a side edge of a back panel to cooperate with a light guide plate in such a way that light emitting from the LED light bar enters the light guide plate from a light incidence surface of the light guide plate and, after being reflected and diffused, is allowed to project out from a light exit surface of the light guide plate to form a planar light source that is supplied to the liquid crystal panel. Due to the advantages of low cost, low power consumption, and being environmental friendly, the edge backlight module has wide applications.
For both the direct and edge backlight modules, when put into operation, the LED light bar gives off heat and the heat affects the performance of the liquid crystal display device for example causing expansion of the light guide plate and thus affecting light homogeneity and shortening the lifespan of the LED light bar. Consequently, the way of dissipating heat plays an important role for a liquid crystal display device. The most direct way is to dissipate heat through the LED light bar. The LED light bar generally comprises a PCB and LED chips mounted on the PCB. Since an ordinary PCB (Printed Circuit Board) is made of FR4 material, which has a low thermal conductivity, generally around 0.3 W/m-k, a metal core PCB (MCPCB) is commonly used to replace a PCB of FR4 material in order to increase thermal conduction performance. The MCPCB shows a thermal conductivity of around 3 W/m-k. However, a MCPCB is formed by bonding a circuit board body and a metal substrate and the LED light bar is mounted to the circuit board body, so that the thermal conductivity of the metal substrate is limited by the circuit board body in the middle, making the thermal conduction performance greatly reduced.